Immunocompromised patients are among the most susceptible individuals to develop invasive candidiasis. Mortality rates among candidemic immunocompromised patients have been estimated at between 38-50%, even with therapy. Currently available diagnostic tests including routine blood cultures lack sensitivity and specificity. Thus, development of innovative laboratory methods capable of providing early evidence of infection and/or complement current cultural and serological tests is imperative. Recent findings from our group suggest that phospholipase B, secreted by Candida albicans may be a novel diagnostic target for candidiasis. This was evident when we tested an isogenic strain pair of C. albicans differing only in their ability to secret PLB, in two different murine models of candidiasis, and showed that the virulence of caplb1 mutants is significantly attenuated. The experiments described in this proposal aim at developing and evaluating Plb1-based diagnostic tests for invasive candidiasis. The overall hypothesis of this proposal is that Plb1 could be useful as a diagnostic marker. In support of this hypothesis, we have shown that Plb1 is secreted and is detectable during host tissue invasion in vivo. Importantly, we also showed that sera from patients with invasive candidiasis (n=33) contained significantly higher levels of anti-Plb1 antibody compared to sera obtained from healthy controls (P = 0.042). We will examine this hypothesis further by pursuit of the following specific objectives: 1) Identification, expression and purification of regions specific to Plb1p deduced amino acid regions. These peptides will be used to evaluate the potential of Plb1 as a specific diagnostic marker. 2) Detection of circulating anti-Plb1p antibody and Plb1p antigen in rabbit sera. 3) Evaluations of diagnostic utility of Plb1p using human sera. The effectiveness of each approach will be evaluated in established experimental animal models of invasive and mucosal candidiasis and patients with culture-proven invasive candidiasis and controls for the study.